In the coated glass industry, it is common to apply one or more thin films onto one or both major surfaces of a glass sheet to impart desired properties in the coated glass. For example, in manufacturing coated glass for windows, it is advantageous to apply infrared-reflective coatings and one or more other coatings that provide hydrophilicity and/or photoactivity.
Insofar as infrared-reflective coatings are concerned, these coatings help provide comfortable interior climates within homes and other buildings. Human beings have a relatively narrow temperature range in which they are comfortable. Unfortunately, infrared (IR) energy from the sun entering a room through a window can quickly raise the temperature in the room to an uncomfortable level. Infrared-reflective coatings have been developed, inter alia, to prevent heat spikes in a room by reflecting some of the incident infrared energy. These coatings also help keep a room warm in the winter by reflecting back into the room some of the infrared energy that would otherwise escape through windows. Thus, infrared-reflective coatings help establish a comfortable living environment while reducing heating and air conditioning costs.
Insofar as hydrophilic and/or photocatalytic coatings are concerned, these coatings have been developed to provide low-maintenance properties for windows and other glazings. These coatings reduce the need for, and/or the effort involved in, cleaning the glass of windows, doors, skylights, and the like. Given the time and effort spent by the average homeowner on window cleaning, the advantages of a low-maintenance window are apparent. Moreover, when one considers the extensive measures and expense involved in cleaning the glass exteriors of modern skyscrapers, the upside of low-maintenance glass can be acutely appreciated.
The foregoing discussion of infrared-reflective coatings and coatings that are hydrophilic and/or photocatalytic is provided merely to exemplify one set of applications for which it is desirable to apply coatings onto both major surfaces of a pane or another sheet-like substrate. The present invention is by no means limited to the application of any particular coating(s). Rather, it has utility in applying a wide variety of thin film coatings. Moreover, the invention is not limited to embodiments in which both major surfaces of a sheet-like substrate are coated. To the contrary, the invention provides numerous embodiments in which only one major surface of the substrate is coated.
It would be desirable to provide methods and coaters in which various coatings can be applied upwardly onto the bottom major surface of a sheet-like substrate. It would be particularly desirable to provide methods and coaters in which coatings can be applied upwardly and downwardly (e.g., in a single pass of the substrate along a path of substrate travel extending through the coater), so as to facilitate rapid and efficient coating of both major surfaces of a sheet-like substrate. Methods and coaters of this nature would be particularly advantageous insofar as they involve applying one or more infrared-reflective films (e.g., a low-emissivity coating) downwardly onto a top major surface of the substrate, and applying another coating (e.g., a hydrophilic and/or photocatalytic coating) upwardly onto a bottom major surface of the substrate.